When organic compounds, particularly polymers or oligomers, are used as electronic device materials, they are often employed in the form of thin films. Examples include insulating films, charge-transporting films, protective films and planarized films.
Organic electroluminescent (EL) devices are expected to see practical application in such fields as displays and lighting, and so various research is being carried out on materials and device structures with the aim of achieving such properties as low-voltage driving, high brightness, and longevity.
A plurality of functional thin films are used in organic EL devices. One such thin film—the hole injection layer, is responsible for transferring charge between an anode and a hole-transporting layer or an emissive layer, and thus serves an important function in achieving low-voltage driving and high brightness in organic EL devices.
Processes for forming the hole injection layer are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. Comparing these processes, wet processes are better able to efficiently produce thin films having a high flatness over a large surface area and therefore are often used particularly in the field of displays.
In light of these circumstances, the inventor and others have developed various types of charge-transporting varnishes containing aniline derivatives or the like as charge-transporting substances (see Patent Documents 1 to 4). However, improvements in the wet process materials for hole injection layers are constantly being sought. In particular, because they can help improve the brightness characteristics or longevity characteristics of organic EL devices, there is a growing desire for materials which provide charge-transporting thin-films of excellent flatness.